Temperature sensing probes, such as thermistors, resistance temperature detectors (RTD's) and resistance thermometers are used in a wide array of applications to provide temperature feedback of various media. In particular, temperature sensing probes are used in industrial process control, engine control, and the like, to measure the temperature of a process or device and provide the measured temperature to a remote device, such as a PID controller, for example. In response to the temperature feedback from the probe, the PID controller may alter system parameters to maintain and/or regulate the temperature of the process or device. Additionally, the temperature feedback from the probe may be used to alarm abnormal conditions (e.g., an over temperature warning).
Temperature sensing probes have what is commonly referred to as a hot end and a cold end. The hot end of the probe is the portion that is inserted into the media in which a temperature reading is desired. The cold end, on the other hand, is the portion of the probe that is used to mechanically mount the temperature sensing probe to a fixed member. The cold end may or may not be inserted in the media. Furthermore, the cold end provides an electrical interface to a remote device, such as a controller or temperature readout.
Temperature sensing probes include numerous components, such as, for example, a temperature sensing element, various wiring, resistors, diodes, switches, etc. Generally, the temperature sensing probe is subjected to harsh environments that easily can damage the components of the temperature sensing probe. Furthermore, the temperature sensing probe is subject to mechanical stress due to vibration from surrounding machinery. To minimize the potential for damage to the probe from environmental and mechanical stress, various packaging schemes have been implemented to protect the measuring circuitry of the probe.
Typically, the packaging schemes employed in temperature sensing probe construction include a sheath or housing, which is typically made of metal, plastic or ceramic. The sheath covers the temperature sensing element and the associated electrical components. The sheath protects the components of the probe from exposure to extreme temperature conditions and/or harsh environments (e.g., chemical environments). The packaging schemes also include intermediate components that attempt to hold electrical components in place and/or attempt to reduce mechanical and/or environmental damage to the probe components. The intermediate components may include greases, thermal greases, rubber, plastic, ceramic and/or metal devices.
Although design safeguards have been implemented in probe construction, environmental and/or mechanical damage still may occur due to various circumstances. For example, mechanical damage may occur to the electrical interface due to mechanical vibration and/or shock, causing fatigue and/or breakage of the electrical interface. Mechanical damage also may occur due to foreign objects striking the temperature sensing probe. Environmental damage may occur due to chemical, mechanical, liquid (e.g., water leakage) or other types of environmental attack. In particular, environmental damage is likely when the sheath has been breached and a contaminant enters the internals of the probe. Breach of the sheath is most likely to occur in the cold end of the probe, particularly where the electrical interface enters/exits the probe. Both environmental and mechanical damage to the probe may result in deterioration or complete failure of the temperature sensing function of the probe.
Some types of heaters are arranged in a similar fashion to the temperature sensing probes described above. For example, one or more heat producing elements (e.g., in the form of a coiled or uncoiled resistance wire, ceramic heater, etc.), along with any desired heat transferring components (e.g., radiating fins) and/or insulators, can be disposed in a sheath. One end of the sheath can be integrally closed with a longitudinal hollow body of the sheath. Integral closures can include unitary construction of the sheath or an end disk mechanically attached to the longitudinal body (e.g., by welding or swaging). An opposite end of the sheath can be sealed in similar fashion to conventional temperature sensing probes to allow conductors, control wires and so forth to exit the sheath and connect to external circuitry. The prior end seals for heaters have been susceptible to damage and/or failure in the same ways cold end seals for temperature sensing probes have experienced damage.
Accordingly, there is a need in the art for an end seal that provides improved sealing and restraining functions for the electrical interface.